view GraphCode.py @ 24:5c2c4ce095ef

A stab at the L(p)/L(0) plot. I still don't quite get how the graphs in the Watts and Strogatz paper were generated. My results have basically the same shape, but don't converge to 0. I'm not sure how this is possible if the rewire function does not remove edges.
author Brian Neal <bgneal@gmail.com>
date Thu, 03 Jan 2013 18:41:13 -0600
parents 04e3a6590139
children
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""" Code example from Complexity and Computation, a book about
exploring complexity science with Python.  Available free from

http://greenteapress.com/complexity

Copyright 2011 Allen B. Downey.
Distributed under the GNU General Public License at gnu.org/licenses/gpl.html.
"""

class Vertex(object):
    """A Vertex is a node in a graph."""

    def __init__(self, label=''):
        self.label = label

    def __repr__(self):
        """Returns a string representation of this object that can
        be evaluated as a Python expression."""
        return 'Vertex(%s)' % repr(self.label)

    __str__ = __repr__
    """The str and repr forms of this object are the same."""


class Edge(tuple):
    """An Edge is a list of two vertices."""

    def __new__(cls, *vs):
        """The Edge constructor takes two vertices."""
        if len(vs) != 2:
            raise ValueError, 'Edges must connect exactly two vertices.'
        return tuple.__new__(cls, vs)

    def __repr__(self):
        """Return a string representation of this object that can
        be evaluated as a Python expression."""
        return 'Edge(%s, %s)' % (repr(self[0]), repr(self[1]))

    __str__ = __repr__
    """The str and repr forms of this object are the same."""


class Graph(dict):
    """A Graph is a dictionary of dictionaries.  The outer
    dictionary maps from a vertex to an inner dictionary.
    The inner dictionary maps from other vertices to edges.
    
    For vertices a and b, graph[a][b] maps
    to the edge that connects a->b, if it exists."""

    def __init__(self, vs=[], es=[]):
        """Creates a new graph.  
        vs: list of vertices;
        es: list of edges.
        """
        for v in vs:
            self.add_vertex(v)
            
        for e in es:
            self.add_edge(e)

    def add_vertex(self, v):
        """Add a vertex to the graph."""
        self[v] = {}

    def add_edge(self, e):
        """Adds and edge to the graph by adding an entry in both directions.

        If there is already an edge connecting these Vertices, the
        new edge replaces it.
        """
        v, w = e
        self[v][w] = e
        self[w][v] = e


def main(script, *args):
    v = Vertex('v')
    print v
    w = Vertex('w')
    print w
    e = Edge(v, w)
    print e
    g = Graph([v,w], [e])
    print g


if __name__ == '__main__':
    import sys
    main(*sys.argv)